As discussed in U.S. Pat. No. 4,833,477, issued to Robert K. Tendler on May 23, 1989, incorporated herein by reference, an emergency vessel or vehicle location system (EVLS) is described in which a mayday message is broadcast via conventional transceivers to all within the broadcast range, with the mayday message including the position of the stricken vessel or vehicle. The EVLS described in the Tendler patent is not limited to vessels or vehicles but may be provided as a unit which is personally carried and is adaptable to hikers or military personnel regardless of their being in a vehicle or not.
One of the problems associated with such radios or modules is the ability to rapidly program such a device for the identification number of a vessel or vehicle. It is important for rescue to have as much information about a vessel or vehicle as possible, both for identification upon reaching the rescue scene and for accountability for false mayday broadcasts.
Secondly, it is important to alert the user that a mayday message is actually being transmitted, as lights or other visual indicators are often times not enough, especially in the ensuing panic at the time of the emergency.
Additionally, a convenient self-test function is useful so that the user can verify the content of the mayday message as well as the actual transmission of the message. Further, the transceiver controlled by the EVLS must be turned on and the appropriate channel selected by the EVLS. Also, adaptability to the digital selective calling (DSC) protocol is a useful feature since verbal mayday messages and the digital mayday messages associated with the DSC protocol can be transmitted sequentially. Also, programmability in a user's voice is useful for additional data to be added to the mayday message. Additionally, guaranteeing that the transceiver goes to high power during the emergency message broadcast is required for maximum range. Further, scrambler lockout is a necessity if the transceiver is provided with a scrambler function. Non-volatile storage of the vessel identification number (VIN) is useful, as is switching to another channel for direction finding (DF) purposes and to permit an added measure of security by being able to continue the mayday broadcast on a non-emergency channel. Finally, inhibiting the EVLS and returning the radio to its normal transceive function with the push-to-talk button is a requirement to permit instant two-way communication.